GB1580411A

GB1580411A - Microwave oven with food temperature sensing means

Info

Publication number: GB1580411A
Application number: GB2001177A
Authority: GB
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1976-05-13
Filing date: 1977-05-12
Publication date: 1980-12-03
Also published as: JPS52137735A

Description

(54) MICROWAVE OVEN WITH FOOD TEMPERATURE SENSING MEANS (71) We, SHARP KABUSHIKI KAISHA, a Japanese company of 22-22, Nagaike-cho, Abeno-ku, Osaka, Japan do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a microwave oven including a food temperature-sensing probe for monitoring an internal temperature of food being cooked in the microwave oven.

A typical food temperature-sensing probe is disclosed in Louis H. Fitzmayer, U.S.

Patent 3,988,930 "Microwave Oven Food Temperature-Sensing Probe", issued on Novenber 2, 1976.

In accordance with the present invention there is provided a microwave oven having a temperature-sensing probe insertable in food in the oven compartment for providing an electrical signal representing the internal temperature of the food, and an oven control unit responsive to said signal, said probe being electrically and mechanically connected to connector means from which the control unit receives said signal, said connector means permitting rotation of said probe in said compartment while said oven is in operation.

Preferably the connector means is on a top wall of oven compartment. Preferably the probe is detachably connected to the connector means.

The invention is particularly advantageous if the microwave oven is provided with a turntable for supporting the food being cooked, in which case the connector means is preferably on the top wall of the oven compartment at a position approximately corresponding to the center of the turntable.

In a preferred embodiment the food temperature-sensing probe is coupled via a flexible, shielded cable to the connector means. The cable may have ajack insertable in a slipping connector structure, or rotatable jack socket, forming the connector means. The probe jack is preferably removable from the slipping connector structure. If the microwave oven has a turntable, the arrangement is such that the probe jack rotates within the connector structure in unison with the rotation of the turntable.

Arrangements embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a microwave oven in accordance with the invention, the oven having a turntable and a food temperature-sensing means; Figure 2 is a sectional view taken on line 1-I in Figure 1; Figure 3 is a sectional view of monitor equipment including a food temperaturesensing probe, a flexible, shielded cable and a probe jack of the food temperature sensing means of the oven; Figure 4 is a sectional view of an embodiment of a slipping terminal unit and a slipping connector structure for securing the probe jack; Figure 5 is a plan view of the slipping terminal unit and the slipping connector structure shown in Figure 4; Figure 6 is an exploded view of the slipping connector structure and the probe jack shown in Figure 4; Figure 7 is a perspective view of the slipping terminal unit shown in Figure 4; Figure 8 is a sectional view of the slipping terminal unit and the slipping connector structure securing the probe jack of another embodiment of the present invention Figure 9 is a sectional view of a microwave oven in accordance with a further embodiment of the invention; and Figure 10 is a diagram showing a food temperature control circuit which can be used in an oven in accordance with the invention.

A microwave oven 1 includes a magnetron 2, a waveguide 3, a fan blade 4, a fan motor 5, a control unit 6, a control panel 7, touch keys 8, an oven light 9, a slipping terminal unit 10, a latched door 11, and a turntable 12 as shown in Figure 1.

The magnetron 2 generates the microwave energy which is transmitted through the waveguide 3 to cook food mounted on the turntable 12 in the oven compartment 24. A power source (not shown) for the magnetron 2 is controlled by the control unit 6 which is operated by the touch keys 8 on the control panel 7 by an operator's fingers. The control unit 6 comprises semi-conductors such as Large Scale Integrated Circuits, Integrated Circuits, etc.

The microwave oven 1 also includes a food temperature-sensing probe 14, a flexible, shielded cable ISa a probe jack 16, a slipping connector structure 17, a turntable motor 18, a shaft 19, and freely rotating rollers 20 as shown in Figure 2. Reference number 13 designates food to be cooked.

The food temperature-sensing probe 14 monitors an inner temperature of the food 13 mounted on the turntable 12 while it is being cooked. The food temperature representing signal provided by the food temperature-sensing probe 14 is transmitted to the probe jack 16 via the flexible, shielded cable 15. The probe jack 16 is rotatably and removably combined with the slipping connector structure 17.

The slipping connector structure 17 is arranged on a top wall 21 of the oven compartment at a position approximately corresponding to the center of the turntable 12 of the microwave oven 1. With such an arrangement the flexible, shielded cable 15 connecting the food temperature-sensing probe 14 to the probe jack 16 is not damaged by the rotation of the food 13 on the turntable 12. The slipping terminal unit 10 is positioned on the slipping connector structure 17.

If the slipping connector structure 17 is not arranged on the top wall 21 at the position approximately corresponding to the center of the turntable 12 of the microwave oven 1, the flexible, shielded cable 15 may be damaged by the rotation of the food 13 mounted on the turntable 12 and, moreover, the smooth rotation of the food 13 may be disturbed.

The flexible, shielded cable 15 is fastended with an adjusting ring 22 made of polysulfone to permit the distance between the food temperature-sensing probe 14 and the probe jack 16 to be adjusted. The turntable motor 18 drives the turntable 12 by means of the shaft 19, said turntable 12 being supported by the frrely rotating rollers 20. The oven light 9 illuminates the oven compartment 24 of the microwave oven I via apertures 23.

Figure 3 shows monitor equipment of the oven. The food temperature-sensing probe 14 is made of electrically conductive material and has a tubular shape, and includes a temperature-sensing element such as a thermistor 25 located within the tip thereof. Said probe 14 has a probe handle 26 attached to a reflector 27.

A core 28 of the flexible, shielded cable 15 has its conductors electrically connected to the thermistor 25 via a lead line 29 in the food temperature-sensing probe 14. Said probe 14 is adapted to be inserted into the food 13 for monitoring the inner temperature therof in such a manner that the reflector 27 is adjacent to the food 13.

A probe jack 16 includes a top electrically conductive member 30 at the tip and having a part which extends along the center axis of the jack and a coaxial tubular electrically conductive member 31.

An insulator 32 in the probe jack 16 is held between the electrically conductive members 30 and 31 to insulate them from each other. Said jack 16 has an indent 45 in the top electrical conductive member 30 just below the tip thereof. Said jack 16 is supported by a jack handle 33 together with the flexible, shielded cable 15. Lead lines 35 and 34 electrically connect the central electrically conductive member 30 and the tubular electrically conductive member 31 to the respective conductors in the core 28 of the shielded cable 15.

The conductors in the core 28 of the flexible cable 15 connect the thermistor 25 to the top electrically conductive member 30 and the tubular electrically conductive member 31, whereby changes in the resistance of the thermistor 25 can be detected by a control unit described below.

The adjusting ring 22 fastens the flexible, shielded cable 15 in a loop, thereby maintaining a preferred overall length of said cable 15 between the said probe 14 and jack 16.

Figure 4 shows the slipping terminal unit 10 and the slipping connector structure 17 securing the probe jack 16. The slipping connector structure 17 comprises a jack socket 36, a jack connector 37 for engagement with the member 30, and a microwave choke structure 38. The slipping terminal unit 10 is provided on the slipping connector structure 17.

The probe jack 16 is inserted into the jack socket 36 which includes the jack connector 37 in a cavity thereof. The top end of the jack socket 36 reaches the center of the slipping terminal unit 10. The jack socket 36, made of an electrically conductive material such as brass, includes a top terminal 44 of electrically conductive material electrically associated with the jack connector 37. The top electrically conductive member 30 of the probe jack 16 is electrically connected with the jack connector 37 at the indent 45 thereof, when said jack 16 is inserted into the jack socket 36. Said jack 16 and said jack socket 36 are fixed to each other so as to rotate in unison.

Two projections 46, 46' extending from the socket 36 engage two projections 56 and 56' extending from the jack handle 33 to couple the jack and the socket together for rotation.

The tubular electrically conductive member 31 is electrically connected with the jack socket 36 at the lower portion of the cavity. The top terminal 44 and the jack socket 36 are insulated from each other by an insulator 51.

An upper sleeve 39 and a lower sleeve 40 are arranged between the slipping connector structure 17 and the jack socket 36 to allow rotation of the jack socket 36 and the probe jack 16 within the sleeves 39 and 40. The upper sleeve 39 supports an upper washer 41 and a lower washer 43 which surround the socket 36 and between which is disposed a snap ring 42 which fits into a grrove in the socket 36. The sleeves 39, 40 and the washers 41, 43 are made of polyacetal resin.

The slipping connector structure 17 made of an electrically conductive material includes the choke structure 38 for preventing the leakage of microwave energy. The length of the choke structure 38 is A/4, wherein A is the wavelength of the microwave energy used in the microwave oven 1. For a microwave frequency of 2450 MHz, A is approximately equal to 4.8 inches, and therefore t/4 equals approximately 1.2 inches.

The slipping connector structure 17 is mounted on the top wall 21 of the microwave oven compartment 24 with screws 47 and 47'. The slipping terminal unit 10 made of polyacetal resin is secured on the top of the slipping connector structure 17 with screws 48 and 48'. The top terminal 44 makes contact with upper slipping terminals 49 and 49', and the jack socket 36 makes contact with lower slipping terminals 52 and 52' at an upper portion 50 of said socket 36. Said slipping terminals 49, 49', 52, and 52' are respectively provided on upper flat spring leaves 53, 53' and lower flat spring leaves 54, 54' which are supported on the sides of the slipping terminal unit 10.

The upper flat spring leaves 53 and 53' are electrically connected with each other by a lead 55, and the lower flat spring leaves 54 and 54' are electrically connected with each other by a lead 55'. Two leads 57 and 57' attached to the upper flat spring leaf 53' and the lower flat spring leaf 54' respectively are electrically associated with control circuitry to control the magnetron 2. The slipping terminal unit 10 is made of polyacetal resin, the slipping terminals 49, 49', 52 and 52' are made of carbon including a metal such as silver, and the flat spring leaves 53, 53', 54, 54' are made of phosphor bronze metal.

Figure 5 shows a plan view of the slipping terminal unit 10 mounted on the slipping connector structure 17. The top terminal 44 is positioned in the center of the slipping terminal unit 10, said terminal 44 touching the upper slipping terminals 49 and 49'. The upper flat spring leaves 53 and 53' are distorted and bear on the top terminal 44 which is wider than the distance provided between the leaves 53 and 53' to ensure electrical connection of the leaves with the terminal. Said upper flat spring leaves 53 and 53' are electrically inter connected by the lead 55. The slipping connector structure 17 is positioned under the slipping terminal unit 10.

Figure 6 shows the slipping connector structure 17 securing the probe jack 16 in an exploded fashion. The slipping connector structure 17 includes the jack connector 37, the upper washer 41, the snap ring 42, the lower washer 43, the upper sleeve 39, and the lower sleeve 40. The choke structure 38 is included within the slipping connector structure 17. The probe jack 16 is inserted into the jack socket 36 within the slipping connector structure 17 for acheiving electrical connection. The top electrical conductive member 30 of said jack 16 is electrically connected to the jack connector 37 in the cavity of said socket 36, and the tubular electrical conductive member 31 of said jack 16 is connected with said socket 36. Said jack 16 is supported by the jack handle 33 together with the flexible, shielded cable 15 and said structure 17 is arranged on the top wall 21 of the microwave oven compartment 24. The projections 46 and 46' are attached to the jack socket 36, and the projections 56 and 56' are attached to the jack handle 33.

Figure 7 shows the slipping terminal unit 10 including the upper flat springs 53, 53', and the lower flat spring 54', which have the upper slipping terminals 49, and 49' and the lower slipping terminal 52' respectively thereon. Said upper flat springs 53 and 53' are inter connected by the lead 55 and the lower flat springs 54 and 54' are inter connected by the lead 55'.

Figure 8 shows the slipping connector structure 17 and the probe jack 16 of another embodiment of the invention.

When the microwave oven 1 is operated for cooking in a condition that the probe jack 16 as shown in Figure 4 is removed from the slipping connector structure 17, the jack socket 36 of said structure 17 is directly exposed to steam or oil from the food 13 cooked in said oven 1. This causes the development of rust or dust on electrical conductive means such as the jack connector 37 and, therefore, an increase of the contact resistance or a reduction of the insulating characteristics will occur. Under these conditions, accurate transmission of the signal to the control unit 6 which includes the control circuitry is disturbed.

A further, improved embodiment of the present invention is shown in Figure 8 which eliminates the above mentioned defects. A protecting cover 58 including an opening 58' at the center thereof is disposed on the top wall 21 of the microwave oven compartment 24. The probe jack 16 and a small part of the jack handle 33 are inserted through the opening 58'. A steel ball 59 is provided in the protecting cover 58 to close the opening 58', when the probe jack 16 is not inserted into the slipping connector structure 17.

When said jack. 16 is inserted within said structure 17, the steel ball 59 is pushed away from said opening 58' to allow the insertion of said jack 16. The steel ball 59 is coated with polyacetal resin for protecting the steel ball 59 from rusting. Thus constructed, the cover 58 will shut out steam or oil generated from the food 13 while it is cooked on the turntable 12 of the microwave oven 1.

In the embodiment shown in Figure 8, the slipping connector structure 17 is firmly mounted on the top wall 21 of the microwave oven, compartment 24, and the probe jack 16 is arranged to be rotated by the food into which it is inserted and which is located on the turntable 12 of said oven 1.

The slipping connector structure 17 is located on the top wall 21 at a position approximately corresponding to the center of the turntable 12. Said structure 17 includes the choke structure 38 and two jack connectors 37, 37', said connectors 37 and 37' being electrically connected to the top electrically conductive members 30 and the tubular electrically conductive member 31 of said jack 16, respectively. The insulator 32 in said jack 16 is held between the top electrically conductive member 30 and the tubular electrically conductive member 31 to insulate them. Said connectors 37, 37' are supported in a fixed insulator 72 made of, e.g. phenol resin.

A sleeve 60 made of polyacetal resin is positioned outside the jack socket 36. The jack socket 36 is electrically connected to jack connector 37'. The jack connector 37 electrically connected to the top electrically conductive member 30 is suspended by an electrically conductive terminal screw 61, said screw 61 combining two insulator plates 62 and 63 which support the jack socket 36.

Said screw 61 is electrically connected to a plate terminal 64 supported by insulator means 65.

A carbon brush 66 having a low coefficient of friction is provided so that it functions to connect the jack socket 36 to a spring 68. The carbon brush 66 is electrically connected to a screw 67 via the spring 68 which is disposed within the insulator means 65, said screw 67 and said spring 68 being made of electrically conductive material. A snap ring 71 sandwiched between two washers 69, 70 made of nylon is positioned on the outside of the jack socket 36 which is rotatably secured in the slipping connector structure 17.

Figure 9 shows another embodiment of a microwave oven 1 in accordance with the invention, including a slipping connector structure 17, a probe jack 16, a food temperature-sensing probe 14, and a flexible, shielded cable 15. The slipping connector structure 17 is fixed on the top wall 21 of the microwave oven compartment 24. The probe jack 16 is rotated in synchronization with the rotation of the turntable 12 via four synchronization gears 73, 74, 75, and 76 with two timing belts 77, 78, said two gears 74 and 75 being mounted on a transmission axis 79. Thus the probe jack 16 is driven to rotate by turntable motor 18.

Figure 10 shows a circuit construction of the microwave oven 1 including a control unit 80 operable to control the temperature of the food 13. The circuit mainly comprises the control unit 80, a slipping connector 81 a temperature-sensing probe 82, a triac 83, and a microwave generator including a magnetron 84. The control unit 80 includes control circuitry incorporating a Large Scale Integrated Circuit 91 etc. Two relays 93, 92 are operated by the Large Scale Integrated Circuit 91 to control the current flow in a gate line 85 and a cook relay line 94 respectively. The relay 92 is provided for switching the power supply and the relay 93 is provided for switching the magnetron energy on and off.

The slipping connector 81 corresponds to the slipping connector structure 17 described above, and the temperaturesensing probe 82 corresponds to the food temperature-sensing probe 14. A temperature signal provided by the temperature-sensing probe 82 is introduced into the control unit 80 via the slipping connector 81, said unit 80 functioning to control a predetermined cooking temperature of the food 13 is positioned in the microwave oven 1.

A gate signal on the gate line 85 produced by the control unit 80 triggers the triac 83 to control the microwave energy of the magnetron 84, said signal corresponding to the predetermined food temperature selected by the control panel 7. The triac 83 with a varistor 87 as a protective device controls current flow to a primary winding of a high voltage transformer 86, said transformer 86 being connected to the magnetron 84 via a capacitor 89 and a rectifier 90 for activating the magnetron 84, and a heater transformer 88 being connected to a filament of the magnetron 84. A power supply side of the circuit includes a commercial power source 95, and a monitor switch 96 which is mechanically placed in its OFF condition when the latched door 11 is closed and is mechanically placed in its ON condition when the door 11 is opened. The power supply side further includes a primary interlock switch 97 and a secondary interlock switch 98, which are mechanically placed in the ON condition when the door 11 is closed and are mechanically placed in the OFF condition when the door 11 is opened through the use of the latch mechanism. That is, the interlock switches 97 and 98 function to allow power to be applied to the remaining portions of the circuit only when the door is tightly closed.

A timer for cooking is set at a desired value through the use of the touch keys 8 included within the control panel 7. When a coil of a cook relay 100 is energized by the relay 92 which is closed by a start switch 99 on the control panel 7, the energization is held and functions to close relay contacts 101, 102. The coil of the cook relay 100 functions to close the relay contact 102 which provides a current path to the oven light 9 and to close the relay contact 101 which provides a current path to the high voltage transformer 86. A fan motor FM for driving the fan blade 4 to draw cooling air through the base of the microwave oven cavity 24 and the turntable motor TTM are also energised.

A stop switch 103 on the control panel 7 is activated by a latch of the door 11. When an open lever provided on the door 11 is operated, the stop switch 103 opens, and the cook relay 100 is opened, which in turn, opens the cook relay contacts 101 and 102 to cut off current flow to the oven light 9 and the high voltage transformer 86. When a memory start switch 104 is activated to recall information in a memory bank, a memorized program in a memory-bank is carried out.

WHAT WE CLAIM IS: 1. A microwave oven having a temperature-sensing probe insertable in food in the oven compartment for providing an electrical signal representing the internal temperature of the food, and an oven control unit responsive to said signal, said probe being electrically and mechanically connected to connector means from which the control unit receives said signal, said connector means permitting rotation of said probe in said compartment while said oven is in operation.

; 2. An oven as claimed in claim I, wherein said connector means is on the top wall of the compartment.

3. An oven as claimed in claim 1 or 2, wherein the probe is connected to said connector means by means which is detachable from said connector means.

4. An oven as claimed in claim 3, wherein detachable means is a jack, and said connector means comprises a rotatably mounted jack socket for receiving said jack.

5. An oven as claimed in claim 3 or 4, including a cover for protecting said connector means from steam or oil in said oven compartment and through which said probe is connected to said connector means, the cover being provided with means for automatically closing the cover when said detachable means is removed from said connector means.

6. An oven as claimed in any preceding claim, wherein said probe is connected to said connector means by flexible, shielded cable, the overall length of which is adjustable.

7. An oven as claimed in any preceding claim, comprising a turntable in the oven compartment and on which food can be supported.

8. An oven as claimed in claim 7, wherein the connector means is mounted on the top wall of the oven compartment at a position corresponding substantially to the centre of the turntable.

9. An oven as claimed in claim 7 or 8, including means for positively rotating the probe in synchronism with the turntable.

10. An oven as claimed in any preceding claim, wherein the connector means has a microwave choke structure.

Il. A microwave oven substantially as herein described with reference to Figures 1 to 7 of the accompanying drawings.

12. A microwave oven substantially as herein described with reference to Figures 1 to 7 as modified by Figure 8 of the accompanying drawings.

13. A microwave oven substantially as herein described with reference to Figures 1

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. magnetron 84, said signal corresponding to the predetermined food temperature selected by the control panel 7. The triac 83 with a varistor 87 as a protective device controls current flow to a primary winding of a high voltage transformer 86, said transformer 86 being connected to the magnetron 84 via a capacitor 89 and a rectifier 90 for activating the magnetron 84, and a heater transformer 88 being connected to a filament of the magnetron 84. A power supply side of the circuit includes a commercial power source 95, and a monitor switch 96 which is mechanically placed in its OFF condition when the latched door 11 is closed and is mechanically placed in its ON condition when the door 11 is opened. The power supply side further includes a primary interlock switch 97 and a secondary interlock switch 98, which are mechanically placed in the ON condition when the door 11 is closed and are mechanically placed in the OFF condition when the door 11 is opened through the use of the latch mechanism. That is, the interlock switches 97 and 98 function to allow power to be applied to the remaining portions of the circuit only when the door is tightly closed. A timer for cooking is set at a desired value through the use of the touch keys 8 included within the control panel 7. When a coil of a cook relay 100 is energized by the relay 92 which is closed by a start switch 99 on the control panel 7, the energization is held and functions to close relay contacts 101, 102. The coil of the cook relay 100 functions to close the relay contact 102 which provides a current path to the oven light 9 and to close the relay contact 101 which provides a current path to the high voltage transformer 86. A fan motor FM for driving the fan blade 4 to draw cooling air through the base of the microwave oven cavity 24 and the turntable motor TTM are also energised. A stop switch 103 on the control panel 7 is activated by a latch of the door 11. When an open lever provided on the door 11 is operated, the stop switch 103 opens, and the cook relay 100 is opened, which in turn, opens the cook relay contacts 101 and 102 to cut off current flow to the oven light 9 and the high voltage transformer 86. When a memory start switch 104 is activated to recall information in a memory bank, a memorized program in a memory-bank is carried out. WHAT WE CLAIM IS:

1. A microwave oven having a temperature-sensing probe insertable in food in the oven compartment for providing an electrical signal representing the internal temperature of the food, and an oven control unit responsive to said signal, said probe being electrically and mechanically connected to connector means from which the control unit receives said signal, said connector means permitting rotation of said probe in said compartment while said oven is in operation.

;

2. An oven as claimed in claim I, wherein said connector means is on the top wall of the compartment.

to 7 as modified by Figure 9 of the accompanying drawings.

14. A microwave oven as claimed in any preceding claim including a control circuit substantially as herein described with reference to Figure 10 of the accompanying drawings.